Vacuum cleaners are widely used to remove dust, particles and debris from a surface. A typical vacuum cleaner comprises a suction head which is connected to a suction source. The suction source usually comprises a suction generator which is operable to generate suction at the suction head to draw in dusted air. The dusted air is delivered to a filtration system where air-borne dust, particles and debris are removed and treated air will be returned to the ambient atmosphere.
Filtration systems that are used in vacuum cleaners are usually divided into the ‘dry’ type and the ‘wet’ type. A dry type filtration system is usually built on a porous filter which operates to block and remove air-borne dust size above a certain size from dusted air when a stream of dusted air passes through the porous filter. A porous filter is referred to as a dry filter herein and usually made of porous materials such as foam, cloth, fabrics, paper or a combination of such materials. The pore size of the porous materials that form a dry filter usually determines the maximum size of particles that can pass through a dry filter. HEPA filter is a typical example of a high efficiency dry filter, with efficiency of up to 99.97%.
While dry filters are widely used in vacuum cleaners, such as domestic, industrial, handheld, stick or tower types, the porosity requirements of dry filters mean that there is always a compromise between air-flow rate and filtering efficiency. Furthermore, dry filters require regular brushing or shaking in order to remove clogging due to deposit of particles on the pores which collectively define the dry filter. A dry filtration system sometimes uses a multiple-stage filter to extend time between cleaning or replacement. A multiple-stage filter typically comprises a coarse filter in combination with a fine filter.
A typical wet filtration system comprises a reservoir of cleansing liquid to facilitate cleansing of dusted air by a cleansing liquid bath. In operation, a stream of dusted air is passed through the cleansing liquid bath and air-borne articles are removed by the cleansing liquid bath. A dust filter comprising a cleansing liquid bath is referred herein as a wet dust filter or a wet filter where appropriate. Although a cleansing liquid bath usually comprises an aqueous based cleansing liquid, the cleansing liquid bath may be formed of cleansing solvents of other bases as and when required.
While wet filtration systems provide a useful solution and is beneficial to facilitate enhanced dust filtering efficiency, the risks that cleansing liquid may spill from a wet filter and/or get into the suction source during operation has somewhat limited applications of wet filtration systems in many types of vacuum cleaners. As a result, wet filtration systems are only found in commercially available upright type vacuum cleaners, and rarely, if at all, found in other types of vacuum cleaners such as the stick or broom type. An upright type vacuum cleaner in the present context is one in which the suction source is housed inside a main housing and the suction head is connected to the main housing by a length of flexible hose such that the suction head can move relative to the main housing to perform vacuuming operation independent of the main housing.
Therefore, it will be beneficial if wet filtration systems are also available in other types of commercially available vacuum cleaners.